This invention relates to the field of blast cleaning equipment. More specifically, it relates to rigging utilized for positioning blast cleaning equipment against the sides of large storage tanks. Such tanks require periodic cleaning in order to remove scale, rust and other debris prior to painting or other surface treatment. This is usually accomplished by means of blast cleaning the surface with suitable abrasives by means of a centrifugal throwing wheel device. Such devices are well known in the art and, for example, may be of the type manufactured by Wheelabrator-Frye Inc. of Mishawaka, Ind.
In order to treat substantially the entire surface of the tank, it is necessary to move the blast device over the circumference of the tank in a uniform manner. For that purpose a number of rigging or suspension schemes have been developed. These include the use of large cranes which are erected and then used to suspend the blast head against the tank sides, or the erection of a scaffolding on the top of the tank to which a rigging or trolley may be attached. In the latter case a crane is also necessary for placing and removing the rigging and for attaching the blast means. Other prior art arrangements are described in the prior art statement of this specification.
In order to lower the cost of blast treating tank sides, it is desirable to provide a blast rigging device which does not require special scaffolding to be installed on the tank nor the use of a crane to erect the rigging. Stated differently, it is desirable to develop a rigging which can "bootstrap" itself up the tank and then lift the rigging in place and subsequently serve to move the rigging and blast head over the surface of the tank. That objective and others are accomplished by the present invention.